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See around corners and use any surface as a mirror
  (+7, -2)
(+7, -2)
  [vote for,

Given that physical surfaces reflect light, such surfaces can be thought of as mirrors of variant levels of perfection. On a reflectiveness scale, a true mirror would be near the top, a glass wall would be pretty reflective and a brick wall would appear to be non-reflective at all.

However, though it appears to be non-reflective, clearly some indirect light is reflecting off it, just like it would be of a mirror wall. It is just too scatered by the surface.

If the wall was a mirror, our eyes would be able to see both the mirror, and the objects around the corner, reflected in the mirror.

The proposed device would be able to analyze the light coming off an arbitrary surface in much the same way.

When pointed at the the brick building at the corner, it would filter out the direct reflection photons, which are describing the wall itself, but keep and amplify the scaterred photons that are desribing the objects around the corner, just as if the brick wall was in fact made of a highly reflective surface.

theircompetitor, Jul 26 2008

See Venus using moon as mirror http://www.space.co...-venus-transit.html
[theircompetitor, May 17 2012]

Camera Can See Around Corners http://science.slas...-see-around-corners
[xaviergisz, May 17 2012]

Coming soon to a phone near you https://www.theverg...-mit-csail-research
[theircompetitor, Oct 09 2017]

Phone cameras getting close to pictures around corners https://www.pcautho...hrough-walls-481698
[theircompetitor, Jan 25 2018]

Baked by Heriot-Watt University https://www.google....t-watt+laser+corner
Pick your own article or video. They use a laser to do this, so that the illumination is known. [notexactly, Feb 03 2018]

Getting ever closer to bakedom https://phys.org/ne...ntists-corners.html
[theircompetitor, Aug 07 2019]

Camera that sees through or around anything https://petapixel.c...or-around-anything/
[theircompetitor, Nov 20 2021]


       So is this a goal or a principle? Need an idea. How does this differ from a mirror? What visual light are you trying to filter out? What sort of analysis would be preformed?   

       So many questions, so sparse an idea...
csea, Jul 26 2008

       Let me attempt to clarify...
theircompetitor, Jul 26 2008

       Interesting, thanks for the clarification, but sounds like magic unless you can describe how to determine the ordering of randomly scattered photons.   

       I can see this working if the wall were covered with an array of small reflectors, pointed in random (but deterministic and known) orientation. A person looking at the wall would just see a mishmosh (that's a technical term,) but the r-oscope could be made aware of the pattern and rearrange to create a sensible image.
csea, Jul 26 2008

       csea, I was thinking of a dark camera chamber with a filter that's taking out direct light but registering side intensity side light.
theircompetitor, Jul 26 2008

       Information and energy are easily separable. This information can not be retrieved in the way you describe. no.
WcW, Jul 26 2008

       //This information can not be retrieved//   

       I dunno. Here are two arguments in opposite directions.   

       a) For. Consider a surface made of two mirrors which are not co-planar (a 'broken mirror'). You could easily "decode" the image reflected from such a surface, based on (i) knowledge of what an image should look like or (ii) the use of a reference image reflected by the surface or (iii) detailed physical measurements of the surface. Now consider a surface made of 100 non- co-planar reflectors. Same thing applies, but it's more difficult. Now consider a surface made of 1 million non-co-planar reflectors, etc etc. The problem becomes more difficult, but at no point completely intractable.   

       b) Against. Light only humours you by appearing to travel in straight lines and reflecting at an angle equal to the incidence. In fact, it does all sorts of weird stuff at the quantum level. The overall effect of light travelling in straight lines etc only works for relatively broad light paths, where all the possible paths can interfere such that the "classical" straight path dominates. In the case of a sufficiently rough surface, this ceases to be the case, and hence light cannot be treated as if it travels in straight lines, reflects at an equal angle etc. Yet, without these assumptions, you can no longer reconstruct the image from the reflection. So, you're screwed at the quantum level.   

       I suspect (b) is right. However, if it's any consolation, I think it ought to be possible to develop a camera that can deconvolute the distorted images seen through patterned (though not frosted) glass.
MaxwellBuchanan, Jul 26 2008

       Yeah, this is an interesting idea, but impossible on any but the simplest surfaces. You'd need to do some kind of X-ray mapping radar on the surface and then then a receiver large enough to collect light from all the reflected angles. Then a computer large enough to reassemble the data into an image.   

       But the piece you are missing is the unknown absorbsion of the surface. If the surface is orange, then it will only reflect light in the orange bands and absorb all others. If you are really unlucky then the surface is black and will radiate all the light in the infrared.
MisterQED, Jul 26 2008

       I think the light source must be stable and well characterized, as well.   

       Consider the scenario consisting of a figure to be imaged (such as a standing human) who is back-lit with our favorite outdoor light source, the Sun.   

       Fortuitous timing, weather, season, etc., could cause a shadow to be projected on the wall so that it would be visible from our observer's location around the corner. On a cloudy day, nighttime, etc., all bets are off.   

       Given the supposed symmetry of the situation, on a different day and sun location, subject and observer might well be transposed!   

csea, Jul 27 2008

       Send in the papperazzi.. if the standing human is Megan merkel in her undies, they will get something off the wall
DDRopDeadly, Jan 25 2018

       Surprising how little she resembles her sister Angela.
MaxwellBuchanan, Feb 03 2018

theircompetitor, Feb 05 2018

       Have you compared them?
pertinax, Feb 06 2018

       //papperazzi// sp "pepperazzi" - the dude at a fancy restaurant walking around with a bazooka-sized pepper mill.
FlyingToaster, Feb 06 2018

       Re. link, well played, [tc].   

pertinax, Nov 20 2021


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